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22
RADIO AGE for January, 1927
The Magazine of the Hour
Dual Impedance Receiver Has Excellent Tone Quality
TONAL quality has always been an aim of the experimenter. In the receiver shown on these pages this objective has been gained by a combination of one stage of audio amplification followed by two stages of impedance coupling. For the distance enthusiast the set has been arranged for one stage of neutralized RF amplification and a regenerative detector. This combination has been tested thoroughly in the laboratory of this magazine and has performed very satisfactorily in all respects, including that of selectivity. This being under the control of the operator, any degree of selectivity may be secured merely by altering the inductive relationship of the RF primary rotor.
As will be noted from the schematic on page 23 the dual impedances (Samson) are a compromise between transformer and impedance coupling. These give good quality reproduction and are mounted and connected in the same manner as ordinary audio transformers, the condensers being already placed inside of the cases.
In the photograph on page 22,
RF and Regeneration Make Ideal DX Set
the condenser on the left is for wavelength tuning, the upper knob on the RF coupler in the center of the panel is for the regenerative rotor, while the lower rotor is for the RF plate rotor which permits either fine or broad tuning. The right hand condenser governs the secondary wavelength. The antenna winding on the coupler at the left is fixed. This coupler is arranged horizontally whereas the double rotor coupler is arranged vertically, this eliminating any possibility of inter-action between inductances.
For neutralization of the first RF tube and to prevent this tube from slipping into oscillation and radiating in the antenna circuit, (even though feebly) the 85 mh choke spanned by a .0001 mfd. fixed condenser is placed in series with the grid return of the first tube and goes to the negative of the first tube. The neutralizing condenser is placed between the plate of the first tube and the grid end of the 85 mh choke. The connection is shown clearly in the schematic circuit printed in this article.
In the regenerative circuit another 85 mh choke is placed in series with the regenerative rotor between the rotor and the primary of the 2 to 1 audio transformer. It prevents RF energy from going through the primary of the audio transformer and being passed on to the next tube, resulting in distortion. This choke is spanned by a .001 mfd •condenser which serves to bypass the RF energy to the filament positive terminal which is common with the ground.
Aside from the features mentioned above the set is a standard, good, radio frequency amplifier with regenerative detector, one straight audio and two impedance stages. The cost of the parts is not excessive and their assembly is simplicity itself.
Pictorial Layout
THOSE who are not accustomed to wiring a receiver from the schematic circuit should consult the pictorial representation of this receiver as shown on page 24. The parts may first be laid out upon the baseboard and the panel as shown in the drawings and the photographs. Then the filament wiring of all the sockets, together with the Am
Front panel view of the receiver described in this article